The objective of this study was to evaluate the switch to once‐daily darunavir/ritonavir 800/100 mg in treatment‐experienced patients with suppressed HIV‐1 replication on a twice‐daily ritonavir‐boosted protease‐inhibitor (bid PI/r) containing regimen, that is in a setting where genotypic resistance test cannot be performed. In this open label, non‐comparative, multicenter study, patients on a bid PI/r‐containing triple combination, with suppressed viral replication, were switched to once‐daily darunavir/r 800/100 mg containing triple combination. The primary endpoint was the proportion of patients with plasma HIV‐RNA < 50 copies/ml 24 weeks after the switch. Intensive darunavir pharmacokinetic evaluation was performed at Week 4 (W4) in 11 patients. Eighty‐five patients were enrolled. All had HIV‐RNA < 50 copies/ml at screening with a pre‐exposure to a median of 2 PI/r (1–5). By intent‐to‐treat analysis (missing = failure), 78/85 patients (92%, 95% CI [83;96]) maintained an HIV‐RNA < 50 copies/ml at W24. Seven patients experienced protocol‐defined treatment failure between baseline and W24: Two had confirmed low‐level viral rebound, one discontinued study treatment for adverse event, three withdrew their consent, and one was lost to follow‐up. By on‐treatment analysis, 78/80 patients (97%, 95% CI [91;99]) maintained an HIV‐RNA < 50 copies/ml at W24. Results were similar at Week 48. The median area under the darunavir plasma concentration–time curve measured in 11 patients was 61,380 ng hr/ml; darunavir median trough concentration 1,340 ng/ml and darunavir half‐life was 12.2 hr. Tolerability of once‐daily darunavir/r 800/100 mg was excellent. Optimally suppressed, treatment‐experienced patients can switch safely from a twice‐daily PI/r regimen to a once‐daily darunavir/r 800/100 mg containing regimen. J. Med. Virol. 85:8–15, 2012. © 2012 Wiley Periodicals, Inc.